The cytotoxic potentials of periodontopathic bacteria will be investigated with specific attention given to Actinobacillus actinomycetemcomitans (A.a.) and other bacteria associated with localized juvenile periodontitis (LJP). The isolation and molecular characterization of several different cytotoxic factors produced by A.a. will be examined first: (1) The leukotoxin (LT) will be further purified and used to determine the mechanisms of LT binding to PMNs and leukocytolysis (2) the proliferation inhibition factor (PIF) will also be isolated, purified and characterized as a necessary first step in determining its molecular basis of action in inhibiting the growth of human gingival fibroblasts (3) another diffusible factor (AFF) that inhibits procaryotic cells associated with gingivitis and plaque formation (Actinomyces viscosus and Streptococcus sanguis) will be purified and the explanation for its bacteriostatic action defined. Monospecific antibody will be prepared for all of these purified cytotoxic factors and subsequently used in the elucidation of their chemical structure and mechanisms of action. The cultural conditions and environmental factors that affect the synthesis of these factors by A.a. will also be determined. Once the details of the A.a. factors have been established we propose to survey other known crevicular bacteria associated with destructive periodontal disease (Capnocytophaga and Eubacterium species, spirochetes, Bacteroides gingivalis and others) for these three kinds of cytotoxic activity. These studies dealing with the direct cytotoxic effects of periodontopathic bacteria on eucaryotic and procaryotic cells offer another kind of approach to understanding (1) the nature of periodontal pathogenesis and (2) ecologic regulation of the crevicular and plaque-associated microbiota.